Add remaining haskell book exercises

1 files changed, 32 insertions, 0 deletions

diff --git a/Haskell-book/21/instances/src/SkiFree.hs b/Haskell-book/21/instances/src/SkiFree.hs
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+++ b/Haskell-book/21/instances/src/SkiFree.hs
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+{-# LANGUAGE FlexibleContexts #-}
+
+module SkiFree where
+
+import Test.QuickCheck
+import Test.QuickCheck.Checkers
+
+data S n a = S (n a) a deriving (Eq, Show)
+
+instance ( Functor n
+         , Arbitrary (n a)
+         , Arbitrary a)
+  => Arbitrary (S n a) where
+      arbitrary = S <$> arbitrary <*> arbitrary
+
+--instance ( Applicative n
+--         , Testable (n Property)
+--         , EqProp a)
+--  => EqProp (S n a) where
+--    (S x y) =-= (S p q) =
+--        (property $ (=-=) <$> x <*> p) .&. (y =-= q)
+instance (Eq (n a), Eq a) => EqProp (S n a) where
+    (=-=) = eq
+
+instance Functor n => Functor (S n) where
+    fmap f (S x y) = S (fmap f x) (f y)
+
+instance Foldable n => Foldable (S n) where
+    foldMap f (S n a) = mappend (foldMap f n) (f a)
+
+instance Traversable n => Traversable (S n) where
+    traverse f (S x y) = S <$> (traverse f x) <*> (f y)